Electromagnetic clutch

ABSTRACT

An electromagnetic clutch capable of reducing attracting noise generated when an armature plate is attracted to the friction surface of a rotor, wherein the thickness of the projected part ( 32 ) of an elastic member ( 31 ) in the state of being compressingly held by an inner plate ( 26 ) and the armature plate ( 12 ) is increased more than the thickness of the projected part ( 33 ) of the elastic member ( 31 ) in the state of being compressively held by an outer plate ( 17 ) and the armature plate ( 12 ), whereby the volume of the projected part ( 32 ) of the elastic member ( 31 ) can be increased relative to that of the projected part ( 33 ).

TECHNICAL FIELD

The present invention relates to an improvement to be made on thestructure of an electromagnetic clutch which is utilized tointermittently supply rotating motive power from a motive power sourcesuch as an engine to a slave device such as a compressor.

BACKGROUND ART

Electromagnetic clutches in the known art include the electromagneticclutch disclosed in Japanese Unexamined Utility Model Publication No. H2-2537. This electromagnetic clutch includes a hub having a flange andconnected to a rotating shaft, an inner plate fixed onto the flange, anarmature plate which is attracted to a rotor member so as to rotatetogether with the rotor member when a field coil is excited, an outerplate fixed onto the armature plate so as to constitute a part thereofand an annular rubber cushion member disposed between the inner plateand the outer plate and fixed onto the two plates.

To describe the electromagnetic clutch in further detail in reference tothe drawings and the like included in the publication, the hub and theinner plate constituted as separate elements from each other areconnected via a rivet. In addition, the surfaces of the outer plate andthe inner plate facing toward the armature plate are aligned along theradial direction. While the portion of the surface of the rubber memberfacing toward the armature plate, which is on the outer plate side, isnot in contact with the armature plate, the portion of the surface ofthe rubber member on the inner plate side facing toward the armatureplate includes a projected part made to project further outward alongthe axial direction relative to the portion on the outer plate side andthe projected part is in contact with the armature plate. The gapbetween the inner plate and the armature plate is eliminated byinserting a washer at the rivet having a measurement along the axialdirection substantially equal to the measurement by which the projectedpart of the rubber cushion member on the inner plate side is made toproject out and then by firmly holding the washer between the armatureplate and the outer plate when locking the armature plate to the outerplate with the rivet.

The extent of the engagement noise that occurs when the armature plateis attracted to and contacts the rotor in an electromagnetic clutchneeds to be minimized. Such engagement noise may be reduced byincreasing the volume of the portion of the rubber cushion member on theinner plate side. However, if the volume is increased in the structureadopted in the electromagnetic clutch disclosed in the publicationquoted above by, for instance, increasing the thickness of the rubbercushion member on the actuator side, the distance between the outerplate and the armature plate is bound to become more significant, whichnecessitates a larger number of washers to fill the gap and leads to aproblem in that the electromagnetic clutch itself and ultimately theslave device such as a compressor cannot be provided as compact units.

In addition, while the extent of the engagement noise is likely to bereduced by fixing the portion of the rubber cushion member on the outerplate side in a compressed state onto the armature plate, the portion ofthe rubber cushion member on the outer plate side is not in contact withthe armature plate in the electromagnetic clutch disclosed in thepublication and thus, the structure achieved by fixing the rubbercushion member on the outer plate side in the compressed state onto thearmature plate cannot be adopted in the electromagnetic clutch in thepublication.

In order to lower the production cost of on-vehicle air-conditioningsystems, electromagnetic clutches need to be manufactured at lower cost,which necessitates the functions of the various parts of theelectromagnetic clutches to be scrutinized thoroughly to eliminate anynonessential parts.

Furthermore, the epoxy coating that is sprayed over the entire rubbercushion member to prevent corrosion normally coats the surface of theprojected part of the rubber cushion member that comes in contact withthe armature plate. In addition, a cationic coating is normally appliedto the armature plate for rust prevention. If the epoxy coating is lefton the contact surface of the projected part of the rubber cushionmember which comes in contact with the armature plate, the projectedpart of the rubber cushion member becomes stuck to the surface of thearmature plate coated with the cationic paint particularly underhigh-temperature, which may prevent the armature plate from becomingattracted to the rotor.

Accordingly, an object of the present invention is to provide anelectromagnetic clutch with which the extent of the engagement noiseoccurring when the armature plate is attracted to the rotor is reduced,the number of required parts can be reduced and the armature plate canbe attracted to the rotor with a higher degree of reliability.

DISCLOSURE OF THE INVENTION

The present invention provides an electromagnetic clutch comprising anexciting coil, a rotor that is rotationally driven by a motive powersource, an armature plate facing opposite the rotor along the axialdirection, which is attracted to the rotor by an electromagnetic forcegenerated as power is supplied to the exciting coil, a hub having anaxial center matching the axial center of the armature plate, an outerplate connected to the armature plate, an inner plate connected to thehub and an elastic member held at an annular gap formed as the outerplate and the inner plate are assembled together and bonded onto boththe outer plate and the inner plate, characterized in that a portion ofthe elastic member on the inner plate side includes a projected partmade to project outward along the axial direction so as to achievecontact with the armature plate when no power is supplied, that holdingportions of the outer plate and the inner plate used to hold the elasticmember face opposite each other over the annular gap and that themeasurement of the holding portion at the outer plate taken along theaxial direction is greater compared to the measurement of the holdingportion at the inner plate taken along the axial direction.

When the electromagnetic clutch adopting the structure described aboveis in an assembled state, the surface of the inner plate facing towardthe armature plate is set further away from the armature plate than thesurface of the outer plate facing toward the armature plate. Thus, theprojected part formed at the portion of the elastic member on the innerplate side is allowed to take on a greater measurement than that in astructure in which the surface of the inner plate facing toward thearmature plate and the surface of the outer plate facing toward thearmature plate are aligned each other along the radial direction in anassembled state. This, in turn, makes it possible to increase the volumeof the projected part at the elastic member.

The present invention also provides an electromagnetic clutch comprisingan exciting coil, a rotor that is rotationally driven by a motive powersource, an armature plate facing opposite the rotor along the axialdirection, which is attracted to the rotor by an electromagnetic forcegenerated as power is supplied to the exciting coil, a hub having anaxial center matching the axial center of the armature plate, an outerplate connected to the armature plate, an inner plate connected to thehub and an elastic member held at an annular gap formed as the outerplate and the inner plate are assembled together and bonded onto boththe outer plate and the inner plate, characterized in that a portion ofthe elastic member on the inner plate side includes a first projectedpart made to project outward along the axial direction so as to achievecontact with the armature plate when no power is supplied, that aportion of the elastic member on the outer plate side includes a secondprojected part which is made to project outward along the axialdirection so as to achieve contact with the armature plate and is alsomade to distend outward along the radial direction so as to be heldbetween the armature plate and the outer plate and that the thickness ofthe first projected part when it is held between the inner plate and thearmature plate is greater than the thickness of the second projectedpart when it is held between the outer plate and the armature plate.

In the electromagnetic clutch adopting the structure described above, agreater thickness achieved at the first projected part of the elasticmember held between the inner plate and the armature plate increases thevolume of the first projected part compared to that in an elastic memberin the related art with the first projected part held between the innerplate and the armature plate and the second projected part held betweenthe outer plate and the armature plate having thicknesses equal to eachother.

As an alternative, the present invention provides an electromagneticclutch comprising an exciting coil, a rotor that is rotationally drivenby a motive power source, an armature plate facing opposite the rotoralong the axial direction, which is attracted to the rotor by anelectromagnetic force generated as power is supplied to the excitingcoil, a hub having an axial center matching the axial center of thearmature plate, an outer plate connected to the armature plate, andinner plate connected to the hub and an elastic member held at anannular gap formed as the outer plate and the inner plate are assembledtogether and bonded onto both the outer plate and the inner plate,characterized in that a portion of the elastic member on the inner plateside includes a first projected part made to project outward along theaxial direction so as to achieve contact with the armature plate when nopower is supplied, that a portion of the elastic member on the outerplate side includes a second projected part which is made to projectoutward along the axial direction so as to achieve contact with thearmature plate and is also made to distend outward along the radialdirection so as to be held between the armature plate and the outerplate and that the thickness of the first projected part in anuncompressed state is greater than the thickness of the second projectedpart in an uncompressed state. The elastic member in thiselectromagnetic clutch can be compressed until the armature contactsurface of the portion of the elastic member on the inner plate side atleast becomes aligned along the radial direction to the surface of theelastic member facing toward the armature on the outer plate side.

By adopting the structure described above in the elastic member of theelectromagnetic clutch, the first projected part, which is allowed tohave a greater thickness, achieves a greater volume relative to thefirst projected part in an elastic member in the related art with thefirst projected part and the second projected part having thicknessesequal to each other in an uncompressed state.

In this electromagnetic clutch, the outer plate includes a passing holeat which a member used to fasten the outer plate to the armature plateis inserted and a projected part projected from the outer edge of thepassing hole toward the armature plate.

The structure described above, which is adopted in the outer plate,precludes the need to dispose a spacer member such as a washer betweenthe armature plate and the outer plate in order to eliminate the gapformed between them due to the difference between the thickness of thefirst rejected portion and the thickness of the second projected part atthe elastic member.

Moreover, the measurement by which the projected part at the outer plateis made to project out is set smaller than the measurement by which thesecond projected part of the elastic member is made to project out. Theelastic member can be compressed until both the surface of the firstprojected part facing toward the armature plate and the surface of thesecond projected part facing toward the armature plate are aligned tothe top surface of the projected part at the outer plate along theradial direction.

In the electromagnetic clutch adopting the structure described above, inwhich the measurement of the projected part of the outer plate issmaller than the measurement of the second projected part at the elasticmember, the second projected part enters a compressed state when theouter plate and the armature plate become connected with each other viathe second projected part and thus, the extent of the engagement noiseoccurring when the armature plate is attracted to the rotor can belowered compared to the extent of the engagement noise occurring in astructure having the second projected member of the elastic member in anuncompressed state held between the outer plate and the armature plate.

As a further alternative, the present invention provides anelectromagnetic clutch comprising an exciting coil, a rotor that isrotationally driven by a motive power source, an armature plate facingopposite the rotor along the axial direction, which is attracted to therotor by an electromagnetic force generated as power is supplied to theexciting coil, a hub having an axial center matching the axial center ofthe armature plate, an outer plate connected to the armature plate, aninner plate connected to the hub and an elastic member held at anannular gap formed as the outer plate and the inner plate are assembledtogether and bonded onto both the outer plate and the inner plate,characterized in that a surface of the armature plate that is subjectedto friction against the rotor is galvanized.

By adopting the structure described above in the armature plate in theelectromagnetic clutch, the transfer torque in the initial stationarystate is improved compared to that in a structure with a non-galvanizedarmature plate and, as a result, the extent of the engagement noiseoccurring as the armature plate becomes attracted to the rotor isreduced.

The armature plate and the outer plate may instead be connected witheach other by forming a projected part at the armature plate so as toproject outward along the axial direction and fitting the projected partat a passing hole at the outer plate. In such an electromagnetic clutch,the armature plate and the outer plate can be coupled without having touse any fastening member such as a rivet.

The hub and the inner plate may be connected with each other by forminga projected part at the hub so as to project outward along the axialdirection and fitting the projected part at a passing hole at the innerplate. In this electromagnetic clutch, the hub and the inner plate canbe coupled without having to use any fastening member such as a rivet.

The electromagnetic clutch is also characterized in that no coating isapplied to the surface of the first projected part at the elastic memberwhich achieves contact with the armature plate when no power issupplied. By adopting this structure in the elastic member of theelectromagnetic clutch, the first projected part does not become stuckonto the surface of the armature plate facing toward the elastic memberhaving a cationic coating applied thereto even when power is beingsupplied, and thus, the armature plate is allowed to be attracted to andheld onto the rotor with a high degree of reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of the overall structure adopted inan electromagnetic clutch according to the present invention;

FIG. 2 is a sectional view of the structure adopted in an assemblyconstituted with the outer plate, the inner plate and the elastic memberin the electromagnetic clutch in FIG. 1, which is not mounted with othermembers such as the armature plate;

FIG. 3 is an enlarged sectional view of the essential portion of theassembly constituted with the outer plate, the inner plate and theelastic member in the electromagnetic clutch in FIG. 1, which is not yetmounted with the other members;

FIG. 4 is an enlarged view illustrating relative dimensional differencesmanifesting in an assembly constituted with the outer plate, the innerplate, the elastic member, the hub and the armature plate in theelectromagnetic clutch; and

FIG. 5 illustrates a state in which the assembly constituted with theouter plate, the inner plate and the elastic member is mounted with thehub and the armature plate, with FIG. 5( a) showing the assembled stateviewed from the side opposite from the rotor, FIG. 5( b) presenting asectional view and FIG. 5( c) showing the assembled state viewed fromthe rotor side.

Reference numerals are used in the figures to indicate specific membersas follows. Namely, reference numeral 1 indicates an electromagneticclutch, reference numeral 2 indicates an exciting coil, referencenumeral 5 indicates a rotor, reference numeral 10 indicates a rotorfriction surface, reference numeral 12 indicates an armature plate,reference numeral 13 indicates an armature plate friction surface,reference numeral 16 indicates a projected part, reference numeral 17indicates an outer plate, reference numeral 18 indicates a holdingportion, reference numeral 19 indicates a flange, reference numeral 20indicates a passing hole, reference numeral 21 indicates a projectedpart, reference numeral 22 indicates a hub, reference numeral 25indicates a projected part, reference numeral 26 indicates an innerplate, reference numeral 27 indicates a base portion, reference numeral28 indicates a holding portion, reference numeral 29 indicates a passinghole, reference numeral 30 indicates an annular gap, reference numeral31 indicates an elastic member, reference numeral 32 indicates aprojected part, reference numeral 32A indicates a surface and referencenumeral 33 indicates a projected part.

BEST MODE FOR CARRYING OUT THE INVENTION

The following is an explanation of an embodiment of the presentinvention given in reference to the drawings.

An electromagnetic clutch 1 adopting the structure schematicallyillustrated in FIG. 1 is utilized to intermittently supply rotatingmotive power from a motive power source such as an engine or a motor toa slave device such as a compressor and comprises an exciting coil 2, arotor 5 that rotates around the exciting coil 2, an armature plate 12facing opposite the rotor 5 along the axial direction, a hub 22 whichrotates as the armature plate 12 rotates, an outer plate 17 connectedwith the armature plate 12, an inner plate 26 connected with the hub 22and an elastic member 31 which is held in an annular gap 30 formed asthe outer plate 17 and the inner plate 26 are assembled together.

To explain the basic operation and the like of the electromagneticclutch 1 adopting the structure described above, the resilience force ofthe elastic member 31 is applied to the armature plate 12 via the outerplate 17 so as to keep the armature plate 12 away from the rotor 5 andthus, the rotor 5 is in a state of idle running when no power issupplied to the exciting coil 2. As power is supplied to the excitingcoil 2, a magnetomotive force is generated, thereby generating amagnetic flux at the rotor 5 and the armature plate 12, which causes thearmature plate 12 to become attracted toward the rotor 5 against theresilience force of the elastic member 31 and ultimately causes theslave device to rotate via the outer plate 17, the elastic member 31 andthe hub 22.

The exciting coil 2, which is wound around a bobbin (not shown) disposedinside a stator housing 3, can be locked to the main body-side housingof the slave device with a mounting plate (not shown). The statorhousing 3 in which the exciting coil 2 is housed, in turn, is housedwith a specific clearance inside an annular groove 4 formed at a sidesurface of the rotor 5 facing opposite the main body of the slavedevice.

The rotor 5 is rotatably fitted around a cylindrical member 9 assumingan annular shape, having a groove 6 formed at the external circumferencethereof at which a connecting belt used to achieve a connection with themotive power source is mounted and axially supporting a drive shaft 8 ofthe slave device via a bearing 7 at the internal circumference thereof.The side surface of the rotor located on the opposite side from the mainbody of the slave device constitutes a flat friction surface 10 that isperpendicular to the axial center and facing opposite the armature plate12 to be detailed below. Slits 11 through which the magnetic fluxgenerated by supplying power to the exciting coil 2 is turned is formedat the friction surface 10.

The armature plate 12 includes a flat friction surface 13 facingopposite the friction surface 10 at the rotor 5. Slits 14, which arealso shown in FIG. 3, are formed at the friction surface 13 of thearmature plate 12 so as to turn the magnetic flux generated by supplyingpower to the exciting coil 2, at a position offset from the position ofthe slits 11 formed at the friction surface 10 of the rotor 5. In thisembodiment, the friction surface 13 at the armature plate 12 isgalvanized over, for instance, a thickness of 8 micrometers. As aresult, the transfer torque in the initial stationary state, which is 40to 50 newtonmeters in the related art with a non-galvanized frictionsurface 13 at the armature plate 12 is improved by approximately 20%.The remaining surfaces of the armature plate 12, other than the frictionsurface 13, e.g., the surface that comes in contact with a projectedpart 32 of the elastic member 31 to be detailed later, are treated witha cationic coating for rust prevention in the embodiment.

As shown in FIGS. 2, 3 and 5, the outer plate 17 is constituted with atubular holding portion 18 used to hold the elastic member 31 andextending along the axial direction and a flange 19 extending outwardfrom the end of the holding portion 18 facing toward the armature platealong the surface of the armature plate 12. The outer plate 17 is lockedonto the armature plate 12 as particularly shown in FIG. 3, by insertinga projected part 16 projecting out from the armature plate 12 at apassing hole 20 formed at the flange 19 and then caulking the head ofthe projected part. Since this structure eliminates the need to use arivet to lock the outer plate 17 to the armature plate 12, a costreduction is achieved with a smaller number of required parts.

The hub 22 is locked onto an end of the drive shaft 8 with a bolt, and,as shown in FIG. 3, the inner plate 26 is connected at a flange 24 ofthe hub 22, which distends along the radial direction from a main body23 of the hub 22 locked to the drive shaft 8. Namely, as illustrated inFIGS. 2 and 5, the inner plate 26 is formed as a separate element fromthe hub 22, having a substantially disk-shaped base portion 27 and aholding portion 28 rising in a substantially tubular shape from theouter edge of the base portion 27 along the axial direction. The innerplate 26 is connected with the hub 22 by first inserting a projectedpart 25 projecting out from the flange 24 of the hub 22 at a passinghole 29 formed at the base portion 27 and then caulking the head of theprojected part 25, as shown in FIG. 3.

Since the hub 22 and the inner plate 26 are formed as elementsindependent of each other as described above, a single inner plate 26can be used in conjunction with various types of devices with varyingdrive shaft diameters and varying positions assumed along the axialdirection, which necessitates the use of different types of hubs 22, andas a result, a cost reduction is achieved. In addition, since the hub 22and the inner plate 26 are locked to each other without using a rivet, acost reduction is achieved with a smaller number of required parts. Itis to be noted that the thickness L2 of the inner plate 26 should bepreferably set larger than the thickness L1 of the outer plate 17, asshown in FIG. 2.

As shown in FIGS. 2, 3 and 5, the elastic member 31 to be detailed belowis disposed in the annular gap 30 formed between the holding portions 18and 27 as the outer plate 17 and the inner plate 26 are assembledtogether, and the outer plate 17 and the inner plate 26 are connected toeach other via the elastic member 31 bonded to both the outer plate 17and the inner plate 26.

As particularly shown in FIG. 5, the elastic member 31 assumes anannular shape ranging along the entire edges of the holding portion 18at the outer plate 17 and the holding portion 28 at the inner plate 26.The elastic member 31 is provided to prevent damage to the drive shaft 8and the like caused by a torque fluctuation by absorbing the torquefluctuation occurring along the rotating direction through torsion. Theelastic member 31 is constituted of a rubber material such as NBR orchlorinated butyl, by ensuring that it can become deformed to such anextent that the volume of the deformed elastic member is approximately82% to 88% of the volume of the elastic member when not deformed. Thus,more reliable torsion of the elastic member 31 is assured.

As shown in FIGS. 2, 3 and 4, the elastic member 31 includes theprojected part 32 formed at a position on the inner plate side, which ismade to project out toward the armature plate 12 and achieves contactwith the armature plate 12 when the armature plate 12 and the rotor 5are at the most distant from each other (i.e., when no power issupplied). The elastic member 31 also includes a projected part 33formed at a position on the outer plate side, which is made to projectout toward the armature plate 12 and extends toward the outer edge alongthe radial direction to be held between the armature plate 12 and theouter plate 17. A surface 34 between the projected part 32 and theprojected part 33 curves inward and thus forms a gap between the elasticmember and the armature plate 12, as particularly shown in FIG. 3. As aresult, the portion of the elastic member 31 that becomes deformed asthe elastic member 31 is compressed is allowed to fill this gap andthus, the compression of the elastic member 31 along the axial directionis facilitated.

While an epoxy coating is applied over substantially the entireperiphery of the elastic member 31 to prevent corrosion, a surface 32Aof the projected part 32 which comes in contact with the armature plate12 is masked during the epoxy coating application and thus remains freeof the epoxy paint. For this reason, even though the cationic coating isapplied onto the surface of the armature plate 12 facing toward theelastic member, as explained earlier, the surface 32A of the projectedpart 32 is not allowed to become stuck onto the surface of the armatureplate 12 facing toward the elastic member when power is supplied.

As shown in FIG. 2, the measurement L5 of the holding portion 18 at theouter plate 17 taken along the axial direction is greater than themeasurement L6 of the holding portion 28 at the inner plate 26 takenalong the axial direction and, at the same time, the outer plate 17 andthe inner plate 26 are assembled together so as to align the front endof the holding portion 18 with the front end of the holding portion 28,according to the present invention. Consequently, the surface of thebase portion 27 facing toward the armature plate is set further awayfrom the armature plate 12 compared to the surface of the flange 19facing toward the armature plate, as shown in FIG. 3. Namely, thedistance to the armature plate 12 from the surface of the base portion27 facing toward the armature plate is relatively large compared to thedistance in the structure in the related art in which the surface of theinner plate facing toward the armature plate and the surface of theouter plate facing toward the armature plate are aligned along theradial direction in an assembled state.

As shown in FIG. 4, the thickness L3 of the projected part 32 is setgreater than the thickness L4 of the projected part 33 at the elasticmember 31 in an uncompressed state, as shown in FIG. 4, so as to ensurethat even when the surface of the base portion 27 facing toward thearmature plate is further away from the armature plate 12 than thesurface of the flange 19 facing toward the armature plate, the elasticmember 31 remains held in a compressed state.

Thus, even when the elastic member 31 is held in a compressed statebetween the inner plate 26 and the armature plate 12, a relatively largethickness of the projected part 32 at the elastic member 31 compared tothe thickness of the projected part of the elastic member on the innerplate side in the compressed state in the related art achieves a greatervolume due to the greater distance to the armature plate 12 from thesurface of the base portion 27 facing toward the armature plate comparedto the corresponding distance in the related art.

As a result, the extent of the engagement noise occurring as thearmature plate 12 becomes attracted to the rotor 5 is lowered. Inaddition, the increase in the volume of the projected part 32 of theelastic member 31 reduces the rates at which the projected part 32 ofthe elastic member 31 becomes buckled and deformed when the clutch isengaged and the armature plate 12 vibrates as a result. For this reason,the projected part 32 of the elastic member 31 does not become damagedreadily.

Furthermore, as shown in FIGS. 2, 3 and 4, an annular projected part 21is formed at the outer plate 17 so as to project out from thecircumferential edge of the passing whole 20. This makes it possible toform the clearance in which the projected part 33 of the elastic member31 is set between the flange 19 of the outer plate 17 and the armatureplate 12 during the assembly process by abutting the top surface of theprojected part 21 against the armature plate 12, as particularly shownin FIG. 3. In the embodiment, the measurement L7 by which the projectedpart 21 is made to project out (i.e., the measurement of the clearancebetween the flange 19 and the armature plate 12) is set smaller than thethickness L4 of the projected part 33 at the elastic member 31 in anuncompressed state, as shown in FIG. 4.

In the structure explained above, the projected part 33 of the elasticmember 31 is held in a compressed state between the flange 19 of theouter plate 17 and the armature plate 12 and, as a result, the extent ofthe engagement noise occurring as the friction surface 13 of thearmature plate 12 is attracted to the friction surface 10 of the rotor 5can be reduced compared to the extent of the engagement noise occurringin a structure in which the measurement by which the projected part 21is made to project out is substantially equal to the thickness of theprojected part 33 at the elastic member 31 and the projected part 33 isheld in a substantially uncompressed state or the projected part issimply in contact with the armature plate 12.

INDUSTRIAL APPLICABILITY

As explained above, according to the present invention disclosed inclaim 1, a structure in which the surface of the inner plate facingtoward the armature plate is further distanced from the armature platethan the surface of the outer plate facing toward the armature plate inan assembled state is achieved, and thus, the projected part formed atthe elastic member on the inner plate side is allowed to project out bya greater measurement relative to that in a structure having the surfaceof the inner plate facing toward the armature plate and the surface ofthe outer plate facing toward the armature plate aligned along theradial direction in the assembled state. As a result, the volume of theprojected part at the elastic member can be increased to lower theextent of the engagement noise occurring when the armature plate becomesattracted to the rotor.

In addition, the increase in the volume of the projected part of theelastic member reduces the rates at which the projected part of theelastic member becomes buckled and deformed when the clutch is engagedand the armature plate vibrates as a result, so as to prevent damage tothe projected part of the elastic member.

According to the present invention disclosed in claim 2, the thicknessof the first projected part of the elastic member held between the innerplate and the armature plate is set greater than the thickness of thesecond projected part of the elastic member held between the outer plateand the armature plate so as to increase the volume of the firstprojected part relative to the volume of the first projected part at theelastic member in the related art in which the thicknesses of the firstprojected part and the second projected part are set equal to each otherand, as a result, the extent of the engagement noise occurring when thearmature plate becomes attracted to the rotor can be reduced.

In addition, the increase in the volume of the first projected part ofthe elastic member reduces the rates at which the first projected partof the elastic member becomes buckled and deformed when the clutch isengaged and the armature plate vibrates as a result, so as to preventdamage to the first projected part of the elastic member.

According to the present invention disclosed in claim 3, the firstprojected part of the elastic member on the inner plate side is allowedto project out to a greater extent than the extent to which the firstprojected part is made to project out in a structure having the firstprojected part of the elastic member on the inner plate side and thesecond projected part of the elastic member on the outer plate sidealigned along the radial direction in a compressed state, so as toincrease the volume of the first projected part relative to the volumeof the first projected part of the elastic member in the related art.Consequently, the extent of the engagement noise occurring when thearmature plate becomes attracted to the rotor is lowered.

Furthermore, the increase in the volume of the first projected part ofthe elastic member reduces the rates at which the first projected partof the elastic member becomes buckled and deformed when the clutch isengaged and the armature plate vibrates as a result, so as to preventdamage to the first projected part of the elastic member.

According to the present invention disclosed in claim 4, the top of theprojected part made to project out from the outer plate achieves contactwith the armature plate and thus, no spacer member such as a washer isrequired to eliminate the gap between the outer plate and the armatureplate, which, in turn, achieves a reduction in the production cost ofthe electromagnetic clutch with a smaller number of required parts.

According to the present invention disclosed in claim 5, the measurementby which the projected part of the outer plate is made to project out isset smaller than the measurement by which the second projected part atthe elastic member is made to project out, so as to ensure that thesecond projected part of the elastic member is held between the armatureplate and the outer plate in a compressed state and, consequently, theextent of the engagement noise occurring when the armature plate becomesattracted to the rotor can be further reduced compared to the extent ofthe engagement noise occurring in a structure in which the secondprojected part is held between the armature plate and the outer plate inan uncompressed state.

According to the present invention disclosed in claim 6, an improvementis achieved in the transfer torque in the initial stationary state bygalvanizing the armature plate, over an electromagnetic clutch in therelated art with a non-galvanized armature plate. As a result, theextent of the engagement noise occurring when the armature plate becomesattracted to the rotor is reduced.

According to the present invention disclosed in claim 7, the armatureplate is connected with the outer plate at the projected part made toproject out from the armature plate, so as to eliminate the need to usea fastening member such as a rivet to connect the armature plate to theouter plate, which leads to a reduction in the production cost of theelectromagnetic clutch with a smaller number of required parts.

According to the present invention disclosed in claim 8, the hub isconnected with the inner plate at the projected part made to project outfrom the hub, so as to eliminate the need to use a fastening member suchas a rivet to connect the hub to the inner plate. This leads to areduction in the production cost of the electromagnetic clutch with asmaller number of required parts.

According to the present invention disclosed in claim 9, even with thesurface of the armature plate facing toward the elastic member treatedwith a cationic coating, the surface of the first projected part of theelastic member is not allowed to stick to the surface of the armatureplate facing toward the elastic member and thus, the armature plate isallowed to be attracted toward the rotor with a high degree ofreliability.

1. An electromagnetic clutch comprising: an exciting coil; a rotor thatis rotationally driven by a motive power source; an armature platefacing opposite said rotor along the axial direction, which is attractedto said rotor by an electromagnetic force generated as power is suppliedto said exciting coil; a hub having an axial center matching the axialcenter of said armature plate; an outer plate connected to said armatureplate; an inner plate connected to said hub; and an elastic member heldat an annular gap formed as said outer plate and said inner plate areassembled together and bonded onto both said outer plate and said innerplate, characterized in: that a portion of said elastic member on theinner plate side includes a projected part made to project outward alongthe axial direction so as to achieve contact with said armature platewhen no power is supplied, with a surface of said projected part, whichachieves contact with said armature plate when no power is supplied,having no coating applied thereto; that holding portions of said outerplate and said inner plate used to hold said elastic member faceopposite each other over said annular gap; that the measurement of saidholding portion at said outer plate taken along the axial direction isgreater compared to the measurement of said holding portion at saidinner plate taken along the axial direction; and that said outer plateincludes a passing hole at which a member used to fasten said outerplate to said armature plate is inserted and a projected part made toproject from the circumferential edge of said passing hole toward saidarmature plate.
 2. An electromagnetic clutch comprising: an excitingcoil; a rotor that is rotationally driven by a motive power source; anarmature plate facing opposite said rotor along the axial direction,which is attracted to said rotor by an electromagnetic force generatedas power is supplied to said exciting coil; a hub having an axial centermatching the axial center of said armature plate; an outer plateconnected to said armature plate; an inner plate connected to said hub;and an elastic member held at an annular gap formed as said outer plateand said inner plate are assembled together and bonded onto both saidouter plate and said inner plate, characterized in: that a portion ofsaid elastic member on the inner plate side includes a first projectedpart made to project outward along the axial direction so as to achievecontact with said armature plate when no power is supplied, with asurface of said first projected part, which achieves contact with saidarmature plate when no power is supplied, having no coating appliedthereto; that a portion of said elastic member on the outer plate sideincludes a second projected part which is made to project outward alongthe axial direction so as to achieve contact with said armature plateand is also made to distend outward along the radial direction so as tobe held between said armature plate and said outer plate; that thethickness of said first projected part when it is held between saidinner plate and said armature plate is greater than the thickness ofsaid second projected part when it is held between said outer plate andsaid armature plate; and that said outer plate includes a passing holeat which a member used to fasten said outer plate to said armature plateis inserted and a projected part made to project from thecircumferential edge of said passing hole toward said armature plate. 3.An electromagnetic clutch comprising: an exciting coil; a rotor that isrotationally driven by a motive power source; an armature plate facingopposite said rotor along the axial direction, which is attracted tosaid rotor by an electromagnetic force generated as power is supplied tosaid exciting coil; a hub having an axial center matching the axialcenter of said armature plate; an outer plate connected to said armatureplate; an inner plate connected to said hub; and an elastic member heldat an annular gap formed as said outer plate and said inner plate areassembled together and bonded onto both said outer plate and said innerplate, characterized in: that a portion of said elastic member on theinner plate side includes a first projected part which is made toproject outward along the axial direction so as to achieve contact withsaid armature plate when no power is supplied; that a portion of saidelastic member on the outer plate side includes a second projected partwhich is made to project outward along the axial direction so as toachieve contact with said armature plate and also made to distendoutward along the radial direction so as to be held between saidarmature plate and said outer plate; that the thickness of said firstprojected part in an uncompressed state is greater than the thickness ofsaid second projected part in an uncompressed state; and that said outerplate includes a passing hole at which a member used to fasten saidouter plate to said armature plate is inserted and a projected part madeto project from the circumferential edge of said passing hole towardsaid armature plate.
 4. An electromagnetic clutch according to claim 1,characterized in: that the measurement by which said projected part ofsaid outer plate is made to project out is set smaller than themeasurement by which said second projected part of said elastic memberis made to project out.
 5. An electromagnetic clutch according to claim2, characterized in: that the measurement by which said projected partof said outer plate is made to project out is set smaller than themeasurement by which said second projected part of said elastic memberis made to project out.
 6. An electromagnetic clutch according to claim3, characterized in: that the measurement by which said projected partof said outer plate is made to project out is set smaller than themeasurement by which said second projected part of said elastic memberis made to project out.